1. Field of the Invention
This invention relates to a semiconductor package accommodating a semiconductor device therein.
2. Description of the Related Art
A semiconductor package comprising a package main body including a base portion having a first surface and a second surface on the side opposite to the first surface, and a semiconductor device accommodating portion provided on the first surface and accommodating a semiconductor device therein; and electric terminals provided in the semiconductor device accommodating portion, electrically connected to the semiconductor device, and exposed on an outer surface of the semiconductor device accommodating portion, has been conventionally known.
A semiconductor device is formed by mounting a desired circuit pattern on a surface of a substrate made from substrate material which is usually silicon, and generates a large amount of heat from the circuit pattern during its operation. When a temperature of the circuit pattern exceeds a certain temperature, the circuit pattern cannot work with its desired performance.
In the conventional semiconductor package, at least the base portion of the package main body is made from material with a high thermal conductivity, for example, copper, aluminum, copper alloy, or aluminum alloy, in order to radiate the heat generated by the semiconductor device. Heat generated by the semiconductor device accommodated in the semiconductor device accommodating portion is transferred to the package main body, mainly to the base portion, and it is further radiated to a material which is in contact with the package main body, mainly with the base portion, for example, a semiconductor package supporting member on which the base portion is placed, air surrounding the package main body, and the other materials.
In recent years where high integration of a circuit pattern mounted on a semiconductor device advances and heat quantity generated by the semiconductor device increases, various structures for improving a heat transfer efficiency of the semiconductor package have been proposed.
JP-A-2004-288949 discloses one example of a structure for improving a heat transfer efficiency as described above. In a semiconductor package disclosed in JP-A-2004-288949, a graphite sheet is brought in close contact with a second surface of a base portion of a package main body. Since the graphite sheet has a high thermal conductivity, heat transferred from the second surface of the base portion of the package main body is diffused rapidly in a direction extending along the second surface, so that a heat transfer efficiency from the base portion of the package main body to a material neighboring thereto is involved.
JP-A-2001-144237 discloses another example of the structure for improving a heat transfer efficiency as described above. In the structure for improving a heat transfer efficiency, a plurality of graphite sheets and a plurality of metal thin plates are laminated alternately. The metal thin plate increases a transfer amount of heat due to its large thermal capacity and the graphite sheet improves heat radiation from the metal thin plate due to its large thermal conductivity.
In the structure for improving a heat transfer efficiency described in JP-A-2004-288949, the graphite sheet is sandwiched between the second surface of the base portion and a predetermined position on a surface of a semiconductor package supporting body when the base portion of the package main body of the semiconductor package is fixed to the predetermined position on the surface of the semiconductor package supporting body by screws, so that the graphite sheet is brought in close contact with the second surface of the base portion and the predetermined position on the surface of the semiconductor package supporting body.
In the fixation utilizing screws as described above, however, uniformity of the degree of the close contact of the graphite sheet to the second surface of the base portion of the package main body of the semiconductor package and the predetermined position on the surface of the semiconductor package supporting body becomes impaired easily. That is, the heat transfer efficiency from the second surface of the base portion to the predetermined position on the surface of the semiconductor package supporting body becomes uneven easily on these surfaces. In addition, the heat transfer efficiency of the graphite sheet in its thickness direction is smaller than that of the graphite sheet in a direction along its surface.
Accordingly, the structure for improving a heat transfer efficiency described in JP-A-2004-288949 can not perform sufficient cooling effect to an increase in heat quantity generated by a semiconductor device in recent years.
In the structure for improving a heat transfer efficiency described in JP-A-2001-144237, the plurality of graphite sheets and the plurality of metal thin plates laminated alternately are mutually brought in close contact with each other using screws, a bonding agent or an adhesive agent to be fixed to each other.
The structure for improving a heat transfer efficiency described in JP-A-2001-144237 is improved in heat radiating efficiency due to an increase in the number of graphite sheets used and the use of the plurality of metal thin plates as compared with that described in JP-A-2004-288949. However, since the alternately laminated graphite sheets and metal thin plates are fixed each other by the screws, the bonding agent or the adhesive agent as described above, the uniformity of the degree of the mutual close contact between the plurality of graphite sheets and the plurality of metal thin plates becomes impaired easily. That is, the mutual heat transfer efficiency between the plurality of graphite sheets and the plurality of metal thin plates becomes nonuniform easily. In addition, the heat transfer efficiency of the graphite sheet in its thickness direction is smaller than that of the graphite sheet in a direction along its surface.
Accordingly, even in the structure for improving a heat transfer efficiency described in JP-A-2004-288949, it can not perform a sufficient cooling effect to the increase of the heat quantity generated by a semiconductor device in recent years. Further, since the alternately laminated graphite sheets and metal thin plates fixed each other by the screws, the bonding agent or the adhesive agent as described above have a relatively large thickness, the thickness of the structure for improving a heat transfer efficiency described above becomes relatively large.